1. Field of the Invention
The present invention relates to an illumination system and a method of forming a fin structure using the illumination system, and more particularly, to an illumination system using an opaque plate including an annular aperture and an aperture dipole as a pupil and a method of forming a fin structure using the same.
2. Description of the Prior Art
With the advancements of semiconductor manufacturing technology, the scale of an integrated circuit is reduced and its operating rate is also faster. In the manufacturing process of the integrated circuit, the key to the technology is the photolithography process, which is responsible for accurately transferring the pattern in a photomask to the various device layers on wafer. In the photolithography process, the pattern in the photomask is mainly projected on a photoresist on the wafer by using an exposure device, so that the resolution of the pattern formed on the wafer, which is called critical dimension (CD), is determined by the exposure device. Since the exposure device transfers the pattern on the photoresist through projection, the reasons to determine CD are the illumination system and a wavelength of the light generated from the illumination system of the exposure device. Accordingly, it's always a task in this field to continuously improve the illumination system to reduce CD.